The semiconductor integrated circuit (IC) industry has experienced rapid growth. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of processing and manufacturing ICs, and, for these advances to be realized, similar developments in IC manufacturing are needed.
Unqualified improvements are not always possible. Often technological advances have drawbacks that must be balanced against the benefits conveyed. These drawbacks may render a refinement that is appropriate for one application undesirable elsewhere. For example, increasing IC device strain improves carrier mobility through the channel region but also increases device leakage. The improved performance is necessary in some applications, whereas the increased leakage is not acceptable in others. Methods of controlling characteristics such as device strain allow designers to manage the tradeoffs posed by modern IC manufacturing techniques.